This invention relates to a flexographic press adapted for short runs and method and, more particularly to a press having plate and anilox rolls each using a dead shaft mandrel about which a sleeve is rotatably mounted and having associated therewith lift means for sleeve removal.
When changing to the next print job on a flexographic printing press, the plate rolls and often the anilox (inking) rolls need to be replaced. This is because the new plates replace those previously mounted on the plate rolls and, in many cases, the ink cell volume on the anilox roll needs to be adjusted for the new print job.
Traditionally, flexographic presses support the inking roller (anilox roller) and plate roller on bearings which open to release the rolls for job change. Once open, the rolls are lifted out of the press using a chain hoist or custom designed robot.
The market for just-in-time print jobs has continued to increase the demand for shorter change times on presses. Likewise, the average job size is rapidly decreasing. This has spawned a new class of press which is narrower than the typical wide-web (30 to 65 inch wide), long run press. The new press is also intended to be quickly changed from one job to the next by only one person.
One solution to fast roll change which is possible on medium width presses (16 to 30 inch wide) is to use plate sleeves instead of plate rolls (i.e., plate sleeves fit over a mandrel whereas plate rolls have bearing journals). Because of the narrower width, these sleeves can be of a weight which can be lifted by hand (10 to 25 lb.). Two types of sleeves have been used. The first style is the "simply" supported plate roller.
In this style, the plate roll consists of a sleeve which is locked onto a mandrel. During printing the roll is rotatably supported in bearings at each side of the press. For sleeve removal, the mandrel is cantilever supported from one side while the opposing bearing is dropped away from the mandrel. This is analogous to unchucking a mandrel in a center winder such as that seen in co-owned U.S. Pat. No. 2,769,600. The plate sleeve is then released from the mandrel and slid sideways to remove it from the press.
The problem with this arrangement is that the deck designs to allow the bearing and support to drop away (giving clearance for removal) are bulky, complex and costly. The problem is aggravated by the operator requirements to connect register control actuators to the roll.
The second style is the "cantilever" supported plate roller. Recently, a press has been developed which only supports the plate and anilox mandrels from one side of the press. This provides natural access for sleeve removal. The major problem with this design is that, for presses wider than about 16 inches, the printing-performance is impaired due to the limited stiffness provided by a cantilever support. Additionally, the mechanism to allow precise adjustment of the roll positions are complex, sensitive and expensive.
The invention avoids the above problems through cantilever mounting a mandrel on which a sleeve is mounted and providing means for raising the mandrel and sleeve to provide advantageous clearance. Further, the sleeve is not fixed to the mandrel but instead rotates on the stationary mandrel (commonly called a dead shaft).